A mechanism for the biochemical regulation of the growth of the corneal epithelium is proposed. It has been established that an increase in the intracellular level of cyclic AMP reduces mitotic activity and cell locomotion, and perhaps enhances the production of basement membrane and the adhesion of cells to the stroma. An increase in the intracellular level of cyclic GMP appears to have the opposite effects. Humoral factors such as catecholamines and prostaglandins discourage cell regrowth and cholinergic agents encourage it. The effects of these first and second messengers and their inhibitors on the regrowth of epithelium is being studied in cultures of corneal epithelial cells. Growth is assessed by counting cells in culture, examination of cellular structure and ultrastructure and by the incorporation of labelled precursors into proteins and nucleic acids.